blk-rq-qos: fix first node deletion of rq_qos_del()

commit 307f4065b9d7c1e887e8bdfb2487e4638559fea1 upstream.

rq_qos_del() incorrectly assigns the node being deleted to the head if
it was the first on the list in the !prev path.  Fix it by iterating
with ** instead.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Josef Bacik <josef@toxicpanda.com>
Fixes: a79050434b45 ("blk-rq-qos: refactor out common elements of blk-wbt")
Cc: stable@vger.kernel.org # v4.19+
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/block/blk-rq-qos.h b/block/blk-rq-qos.h
index c0f0778d5396fecfd725d4085bd2837f7a2f4e81..8378f68a21ac013630110cc1e4b401660cb6e8c0 100644 (file)
--- a/block/blk-rq-qos.h
+++ b/block/blk-rq-qos.h
@@ -103,16 +103,13 @@ static inline void rq_qos_add(struct request_queue *q, struct rq_qos *rqos)
 
 static inline void rq_qos_del(struct request_queue *q, struct rq_qos *rqos)
 {
-       struct rq_qos *cur, *prev = NULL;
-       for (cur = q->rq_qos; cur; cur = cur->next) {
-               if (cur == rqos) {
-                       if (prev)
-                               prev->next = rqos->next;
-                       else
-                               q->rq_qos = cur;
+       struct rq_qos **cur;
+
+       for (cur = &q->rq_qos; *cur; cur = &(*cur)->next) {
+               if (*cur == rqos) {
+                       *cur = rqos->next;
                        break;
                }
-               prev = cur;
        }
 
        blk_mq_debugfs_unregister_rqos(rqos);